<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

<div id="app">

    <h2>{{counter}}</h2>
    <button v-on:click="counter++">+</button>
    <button v-on:click="counter--">-</button><br>
    <button v-on:click="increment">+</button>
    <button @click="decreament">-</button>
</div>


<script src="../../js/vue.js"></script>

<script>
    const vue = new Vue({
        el: "#app",
        data: {
            counter: 0
        },
        methods: {
            increment () {
                this.counter++;
            },
            decreament () {
                this.counter--;
            }
        }
    });
</script>

</body>
</html>